Burnout: the art of doing the bare minimum. It's like the opposite of productivity, where one's enthusiasm is not just waning, but extinguished. Like a fire that's been smothered by a damp sponge.
Imagine being so unenthusiastic that you'd rather be a sloth than a human. That's burnout in a nutshell.
It's not just a state of mind, but a lifestyle. A lifestyle where you're constantly wondering, "Do I really have to do that?" and the answer is always, "Ugh, I guess."